The third season of Bungo Stray Dogs opens with a flashback arc set during Osamu Dazai's days in the Port Mafia, tracing how he first crossed paths with Chuya Nakahara and the case that bound them together. The present-day episodes resume with the Armed Detective Agency and the Port Mafia both drawn into a scheme orchestrated by Fyodor Dostoevsky, leader of a group called Rats in the House of the Dead.